Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
CA 02415450 2005-07-11
Read-Only Optical Recording Medium with Zn0 Near-Field
Optical Interaction Layer
s
to
Field of the invention
is
This invention is a read-only near-field optical disk using a zinc-oxide
(Zn0) nano-structured thin film as the localized near-field optical
interaction
layer. Ultrahigh density near-field recording can be achieved by this read-
only
optical disk.
Background of the invention
The conventional optical disks are practical and popular in optical
recording media with fine storage quality and high stability, which have been
2s widely utilized for data storage and multimedia entertainment. Accompanying
with the advanced technological development, a mass amount of disks are
I
CA 02415450 2002-12-30
produced into lots of categories and features, mainly divided into three
types,
read-only, write-once, and rewritable. The read-only type disks are CD-DA,
CD-ROM, CD-l, VCD, DVD-ROM, DVD-Video etc. The write-once type disks
are CD-R, DVD-R and so on. The rewritable disks are MD, MO, PD, CD-RW,
DVD-RW, CD-RAM etc.
A pre-recorded disk is also called a read-only disk. The fabrication of
read-only disk is to lithograph pre-recorded recording-pits as the recorded
marks on a transparent substrate and then subsequently coated the reflection
layer and protection layer by sputtering or spin-coating. The recorded marks
can be read and retrieved by the reflected optical signals of the focused
laser
light delivered and collected by the pick-up head lens of the optical disk
drive.
Currently, the distance between the optical disk and the pick-up head lens is
much larger than the wavelength used by the optical disks and disk drives
commercially available. That means fihe optical recording technology is using
far-field optics alone. It is unavoidable that an optical interFerence or
diffraction phenomena will occur due to the wave characteristics of optics,
and
the spatial resolution of recording and reading is limited by the optical
diffraction limit (i.e. 1.22a/2nsin8, where ~f is the wavelength of the light
used, n
is the refractive index of the medium, and B is the half angle of the
aperture). In
the past, the following methods were used to increase the recording capacity
of the conventional optical disks:
(1 ) A more efficient coding and decoding technique.
(2) A smaller size of all the pits and their pitches of the tracks on optical
disks.
(3) Use of the shorter wavelength of light source.
25(4) Increase of the numerical aperture value of the objective lens.
(5) Use of the volumetric technology such as mufti-layer recording,
holography,
2
CA 02415450 2005-07-11
etc.
Aforementioned methods are only the optimizations under the diffraction
limit of far-field optics. A most basic way to improve the recording density
and
break through the diffraction limit is the use of the near-field optical
technology.
Eric Betzig of the Bell Laboratory, USA, first demonstrated the near-field
optical recording using an optical fiber probe in 1992. His results overcome
the optical diffraction limit. The recorded density was effectively improved.
An optical fiber probe with an aperture of several tens of nanometer at the
fiber
end is used for the near-field optical recording and readout on a multi-
layered
platinum (Pt) and cobalt (Co) magneto-optical medium layer in his work. By
controlling the fiber probe in a very close distance which is much smaller
than
the wavelength used for the experiments, an ultrahigh density recording of 45
Giga-bits per square inch was achieved. However, there are several
difficulties
and disadvantages of using the near-field fiber probe such as the precise
control of the distance between the fiber probe and surface of the recording
medium (about a few nanometers), the fragility of the fiber probe, low
scanning
speed, low optical throughput and high optical attenuation (around 10-s to 10-
3),
and complexity of the fabrication of the nanometer-scale aperture at the end
of
the fiber probe.
On the other hand, an issued USA patent, No. 5, 125,750, disclosed a
solid immersion lens (SIL) prototype that was possible and practical to
implement the near-field disk drivers by G. S. Kino and his research team on
the Stanford University, USA. The method of said patent has a reading/writing
head which made of the semi-spherical and the super semi-spherical
transparent solids -- which have a high reflection index, n, -- for effective
shrinking the reading/writing marks. Thus, said method of optical head could
3
CA 02415450 2002-12-30
be speeding a readinglwritingrate, then by adopting present
the disk
technology to directly developinto the high density recording
optical of
near-field diskdrivers. In a company named TeraStorin San
1995, Jose,
California, patented technological
USA adopted SIL as a "flying"
this
reading/writingpick-up head disk drivers,
to the near-field
optical recording
and tried to produce a first optical disk drive in high density optical
recording.
This high-speed "flying" readinglwriting pick-up head had to be efFectively
controlled under a near-field range. The technical problems of the reliability
of the flying pick-up head in the optical near field finally hindered the
further
developments of the high density near-field optical disk driver.
The issued patents of USA: No. 6,226,258; 6,242,157; 6,319,582 and 6,340,
813, in which Dr. Junji Tominaga disclosed a design, by adding two nano-film
layers (SiN in 20 nm and Sb in 15 nm) onto the normally used phase-change
optical disk to replace the near-field effect of an optical fiber probe of the
near-field scanning microscope, and to carry out the readlwrite actions beyond
the optical diffraction limit.
Aforesaid design show a usage of alternating of thin-film structure on the
disks to reach a near-field ultra high density of optical recording. Then
accompanying with an improved structure of the film layer of said disks, said
~ structure improved the two main structures of said film layer from a first
category (Sb and SiNx,) to a second category (AgOx and ZnS-Si02~. However,
said film layer of said two categories, which generated a localized near-field
optical effect of Sb and AgOx narro-film layer, of their substanceslmaterials
are
unstable, and can easily lose the properties of localization due to high
temperature and the absorption of water vapor.
The present invention is a read-only near-field optical disk with a zinc-oxide
4
CA 02415450 2002-12-30
(Zn0) nano-structured thin film and a spacer layer such as ZnS-Si02 on the
pre-recorded substrate. The ultrahigh density read-only near-field recording
disk can be effectively achieved by this invention.
In summary, aforementioned conventional far-field optical method
appears that the short-wavelength of light-source is costly, and the
reading/writing spots of a conventions! disk driver have an optical
diffraction
limit, so only the near-field optics with no diffraction limits can
effectively
improve the recording spot size below the diffraction limits. Additionally,
the
near-field optical technique of aforesaid near-field scanning probe and SIL
near-field optical disk drive have lots of difficulties, which makes said near-
field
optical disk become an appropriate choice for near-field optical recording. It
is
known that Sb and AgOx are unstable substanceslmaterials for manufacturing
disks, so this invention uses more stable and better localized near-field
optical
effect of zinc-oxide (Zn0) nano-structured thin films) to produce the read-
only
zinc-oxide (Zn0) near-field optical disks. This invention is to use the
stability
and the localization effect of the zinc-oxide (Zn0) nano-structured thin film
along with a near-field spacer layer of ZnS-Si02 to achieve an ultrahigh
density
near-field optical disk. The localized near-field optical effects can be
happened between the zinc-oxide (Zn0) nano-structured thin film and
pre-recorded pits or marks on a transparent substrate in near-field range.
There is no diffraction limit for the read-only optical storage using this
method.
Summary of the Invention
2s This invention is related to a zinc-oxide (Zn0) nano-structured thin film
used in read-only near-field optical disks. Because the near-field optical
s
CA 02415450 2005-07-11
interactions have no diffraction limits, this read-only near-field optical
disk is
capable of obtaining ultrahigh recording density and capacity.
The zinc-oxide (Zn0) nano-structured thin film is fabricated along with a
near-field spacer layer of ZnS-Si02 on a transparent substrate with
pre-recorded recording pits. The localized near-field optical interactions
between zinc-oxide (Zn0) nano-structured thin film and the pre-recorded pits
on the substrate enable the ultrahigh spatial resolution readout of the
pre-recorded pits smaller than the optical diffraction limit.
Another object of this invention is to provide various range of optimal
thickness for said nano-structured thin film layers for a better localized
optical
effect or interaction under a stable operating circumstance.
Another object of this invention is to provide a structure of multilayered
thin film with metallic or glass, or the materials for supporting a process of
localized near-field optical effect in readout of the pre-recorded pits or
marks.
Brief Description of the Drawings
For a better understanding of the present invention as well as other
objects and features, reference is made to disclose this invention taken in
conjunction with drawings as follows.
FIG. 1 is a structural diagram showing the read-only optical recording
medium with zinc-oxide (Zn0) near-field optical interaction layer for disks in
this invention.
FIG. 2 is a schematic illustration showing the working principle of the
read-only optical recording medium with zinc-oxide (Zn0) near-field optical
6
CA 02415450 2005-07-11
interaction layer for disks in this invention.
FIG. 3 is a schematic illustration showing one preferred embodiment of the
pick-up head and optical lens of a disk driver in coordination with the read-
only
optical recording medium with zinc-oxide (Zn0) near-field optical interaction
layer of optical disk in this invention.
FIG. 4 shows the readout results of the pre-recorded marks of the
read-only optical disk with zinc-oxide (Zn0) near-field optical interaction
layer
by using an optical disk tester.
Description of the Preferred Embodiments
The following descriptions of the preferred embodiments are provided to
understand the features and the structures of the present invention.
Figure1 is a structural diagram of the read-only optical recording medium
with zinc-oxide (Zn0) near-field optical interaction layer for disks according
to
present invention. The structure of the read-only optical recording medium
comprises a transparent substrate 2 with pre-recorded pits or marks 1 and a
plurality of thin film layers formed on said a transparent substrate 2 with
pre-recorded pits or marks 1. The plurality of thin films consist of a
reflection
thin film layer 3, a first transparent dielectric thin film layer 4, a zinc-
oxide (Zn0)
nano-structured thin film layer 5 which is capable of causing localized
near-field optical interactions, and a second transparent dielectric thin film
layer 6. The transparent substrate with the pre-recorded pits or marks is
made of Si02 glass material or doped Si02 glass material with Sodium(Na),
Lithium (Li), Calcium (Ca), Potassium (K), Aluminum (AI), Germanium (Ge),
CA 02415450 2005-07-11
and Boron (B), etc. in various ratio, or transparent polymerized materials
which
comprise polycarbonate, or epoxy resin, etc, The pre-recorded pits or marks
1 are lithographed for prerecording, and the dimension of said pre-recorded
pits or marks1 can be smaller than the optical diffraction limit. The material
of
said reflection thin film layer 3 is selected from a group or an alloy group
consisting of Gold (Au), Sliver (Ag), Aluminum (AI), and Copper (Cu). The
first transparent dielectric thin film layer 4 and the second transparent
dielectric
thin film layer 6 can be a multiple layered structure selected from the group
of
the transparent dielectric materials consisting of ZnS-Si02, ZnS-SiOx, Si02,
SiOx, or SiNx. The optimal thickness of the first transparent dielectric thin
film
layer 4 and the second transparent dielectric thin film layer 6 is in a range
of
about 5nm to 200nm. The zinc-oxide (Zn0) nano-structured thin film layer 5
that is capable of causing localized near-field optical effect is made of the
compound of zinc-oxide (Zn0), or the compositions of zinc-oxide (Zn0) and
zinc. The optimal thickness of the zinc-oxide (Zn0) nano-structured thin film
layer 5 is in the range of 5nm to 100nm.
Figure 2 shows the working principle of the read-only optical recording
medium with zinc-oxide (Zn0) near-field optical interaction layer for disks
according to the present invention. The light beams (in/out) 7 of light source
via the optical lens 9 of a pick-up head of disk driver 8 penetrate pre-
recorded
pits or marks 1 of transparent substrate 2, reflection thin film layer 3 and
the
first transparent dielectric thin film layer 4 thereto focusing on zinc-oxide
(Zn0)
nano-structured thin film layer 5 which is capable of causing localized
near-field optical interactions. The localized near-field optical interaction
beyond diffraction limit 10 generated by the interaction of the focused laser
and zinc-oxide (Zn0) nano-structured thin film layer 5 can interact with the
s
CA 02415450 2002-12-30
recorded pits or marks after thin film coating 1' to read the storage data of
said
recorded pits or marks after thin film coating 1'. For the content of said
recorded pits or marks after thin film coating 1' is the same as the content
of
said pre-recorded pits or marks 1 of said transparent substrate 2. That is to
say, the content of said pre-recorded pits or marks 1 can be read out.
Therefore, accompanying with a rotating disk and a high-speed readout
scanning optical head of a disk driver, the readout action of ultrahigh
density
read-only optical recording medium can be carried out. The first transparent
dielectric thin film layer 4 and the second transparent dielectric thin-film
layer 6
can protect and stabilize the zinc-oxide (Zn0) nano-structured thin film layer
that is capable of causing localized near-field optical interactions 5, and
maintain a fixed near-field distance between said recorded pits or marks after
thin film coating 1' and said a zinc-oxide (Zn0) nano-structured thin film
layer
that is capable of causing localized near-field optical interactions 5.
As shown in Fig. 3, it is a preferred embodiment of a read-only zinc-oxide
(Zn0) near-field optical disk 11 and pick-up head of disk driver 8. The
pick-up head of disk driver 8 maintains the readout focusing at co-planarity
and
co-track of said read-only zinc-oxide (Zn0) near-field optical disk 11 by
current
tracking and focusing technology of the disk driver, and the read-only
zinc-oxide (Zn0) near-field optical disk 11 rotates in the rotation direction
of
optical disk 12. The localized near-field optical interaction beyond
diffraction
limit 10 coupled between zinc-oxide (Zn0) nano-structured thin film layer that
is capable of causing localized near-field optical interactions 5 and recorded
pits or marks after thin film coating 1' can successfully readout said
pre-recorded pits or marks 1 formed on transparent substrate 2 in said
read-only zinc-oxide (Zn0) near-field optical disk 11.
9
CA 02415450 2002-12-30
One of the experimental readout results of the read-only zinc-oxide (Zn0)
near-field optical disk 11 is displayed in Fig. 4. A disk tester (manufactured
by
Pulstec Industrial Co., Ltd., Model DDU-1000) with the wavelength of light
source at 673 nm and numerical aperture (NA) of the pick-up head lens at 0.6
is used to readout the pre-recorded 100 nm marks on a read-only zinc-oxide
(Zn0) near-field optical disk 11 in this invention. The disk is rotated in a
constant liner velocity at 3.5 mls, and the readout laser power out of the
pick-up head is 4 mW. The readout results measured by a spectrum analyzer
is shown in Fig. 4. The measured carrier-to-noise (CNR) value of the
pre-recorded 100 nm marks is 31.82 dB. It is clearly evident that read-only
zinc-oxide (Zn0) near-field optical disk 11 described in this invention is
capable of recording pre-recorded pits or marks below the optical diffraction
limit.
While this invention has been described in conjunction with particular
embodiments, it is evident that alternatives, modifications and variations
will
now be apparent to those skilled in the art. Accordingly, the present
invention is
intended fio embrace all such alternatives, modifications and variations and
fall
within the spirit and scope of the appended claims. Moreover, the description
and illustration of the invention is by way of example, and the scope of the
invention is not limited to the exact details shown or described as well as
the
order of structure, the values, angles, directions of focusing beams.
io
